NER: Mesogeochemistry ù Geochemical Reactions and Mass Transfers in Nano-scale Pore Space Confinement

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Xu & WangNER-0210820This proposal was received in response to the Nanoscale Science and Engineering initiative NSF 01-157, category NER, and is co-funded by the GEO Directorate.The emergence of nanotechnology has made it possible to manipulate material structures at nanometer scales and has greatly advanced our understanding of how these nano-scale structures give rise to novel physical and chemical properties not seen in bulk materials. Nano-scale pore structures, also called mesoporous structures, are ubiquitous in geologic and engineered materials. Our preliminary studies, both experimentally and theoretically, indicate that chemical reactions in mesopores can be significantly modified, both thermodynamically and kinetically, due to the nano-scale confinement. The objective of this proposal is to (1) clarify the sorption behavior of chemical species in a nano-scale pore space confinement as compared to that in bulk solutions and test the hypothesis that metal sorption on mesopore surface can be greatly enhanced by the confinement effect; and (2) to determine the rates of aqueous species diffusion in nano-scale channels to test the assumption that these channels can provide passages for mass transport during chemical reactions.To isolate the effect of nano-scale pore space confinement, we will conduct parallel sorption experiments on non-mesoporous materials, and the measured sorption capabilities will be compared between mesoporous vs. non-mesoporous materials. Particular attention will be paid to the possible effect of electric double layer (EDL) overlap in mesopores on ion sorption and diffusion. Based on the experimental data, a new surface complexation model will be proposed to explicitly include the effect of EDL overlap. The issues to be addressed in this proposal are fundamental, and the proposed work will highly impact many aspects of geochemical research. The proposed research will establish a theoretical foundation for the development of high-performance functional materials for solving challenging environmental issues we are facing today.